From my perspective, the worst part about plans is a lack of formed or molded parts such as cowls, pants and of course windshields/windows/canopies.
Yes, it can all be accomplished, but the complexity of a project easily gets to be too much to bother with and this is coming from someone who actually enjoys building.
Since kits seem to have all but disappeared, the current scale kit project that I'm working on will probably be my last.